An automobile assembly plant can have at least three main areas: the body shop, the paint shop and the assembly area. Assemblies including automotive car bodies, panels and large parts are conveyed from the body shop to the paint shop. After entering the paint shop, the assemblies require a series of metal pretreatment processes, including surface cleaning, conversion coating, and primer paint electrodeposition. In many instances, the assemblies are formed from bare steel structures and panels that are combined together using known processes. Prior to passing the assemblies to the sealer area and finally to the decorative topcoat paint application, the assemblies are hung from a conveyor and passed through several spray stations, draining stations, immersion tanks, drying stations and, finally, a baking oven to dry an electrodeposited primer material. The processes prior to the baking oven can consist alternately of several spraying, draining, drying and immersing zones. The length of the zones can vary and are generally based on production throughput and corresponding conveyor speed. The number of zones is extensive and a typical paint shop may have in the range of 40 such zones or steps in the overall process. The amount of space required for this overall process is large and can require a building size of approximately 16,000 m2. The amount of water and energy required for this process makes it attractive for efficiency improvement.
Various attempts to improve the processes in the pretreatment and electrodeposition area of the paint shop have been considered. In certain efforts, one to three additional degrees of freedom have been added to the conveyor so that the assemblies can be immersed in a non-horizontal position and rotated vertically or horizontally while entering in or leaving the immersion tank. Other efforts have included improvements in the electrical contact with the assemblies during the conveying process. More recent advancements include the motorization of each assembly carrier and the electrical isolation of the assemblies from the conveyor or grounded contact. The more recent advancements have mostly targeted the processes involving the primer paint electrodeposition immersion tank. Only minor process improvements in the cleaning, conversion coating and rinsing processes have been realized.
While some of these process changes have provided improvements in the process, the additional cost, complexity, and maintenance requirements do not always merit changing from the traditional approach. As one example, each conveyance carrier must have a significant cost increase to provide the additional rotary axis. Additionally, the rotational component can be subjected to harsh conditions while it is often submerged with the assembly. Paint must be occasionally stripped from the submerged portion of the part holding carriers and since they are now more geometrically complex, the paint is more difficult to remove. The harsh environment also requires additional maintenance on the submersed portion of the rotary joint, including greasing, seal replacement, and electrical contact repair.
It would be advantageous if the paint shop processes could be improved while at the same time reducing capital cost and improving system maintainability.